Fix bug in DockerAuth 'unmarshal'
Fix bug in DockerAuth 'unmarshal'

aws/amazon-ecs-agent,kiranmeduri/amazon-ecs-agent,aws/amazon-ecs-agent,jaimeguzman/amazon-ecs-agent,kiranmeduri/amazon-ecs-agent,seiffert/amazon-ecs-agent,aws/amazon-ecs-agent,kiranmeduri/amazon-ecs-agent,swipely/amazon-ecs-agent,kiranmeduri/amazon-ecs-agent,swipely/amazon-ecs-agent,swipely/amazon-ecs-agent,aws/amazon-ecs-agent,jaimeguzman/amazon-ecs-agent,swipely/amazon-ecs-agent,seiffert/amazon-ecs-agent